(1) Field of the Invention
The present invention relates to a metallically decorated sheet, which adds metallic appearance to a, surface of a resin product or resin part such as an interior or exterior decor of a motor vehicle, furniture, building material, bag, household appliances, audio, personnel computer, portable telephone, personnel digital assistant (PDA), camera, video camera, signboard, display, name plate, architrave, amusement product such as pinball machine and slot machine, cosmetic case, jewel, tableware, and toy.
(2) Description of the Related Art
A molded product having a metallic appearance on its surface, which is produced by inserting a metallically decorated sheet into a mold upon molding of a molded resin, can replace an ordinary metallic material with maintaining a feeling of quality and at the same time attain the process saving, decrease in the cost, and weight saving. Consequently, the metallically decorated sheet meets the current demand and various technologies have been proposed mainly in the field of non-structural parts.
A general structure of a metallically decorated sheet is schematically illustrated in FIG. 4. A metallic layer is formed on one side of a transparent or translucent thermoplastic resin film by using vacuum-applied technology such as vacuum evaporation method, sputtering method and ion plating method, and a film having the metallic layer is stuck to a thermoplastic resin film as the base film putting an adhesive layer therebetween, thereby the metallically decorated sheet is produced.
For the purpose of protecting the metallic layer, an extremely thin film can not be used as the transparent or translucent thermoplastic resin film.
A cost of forming the metallic layer accounts for a main part of the production cost of the metallically decorated sheet. The greater part of the cost of forming the metallic layer is attributed to a cost of setup processes.
The formation of the metallic layer by using the vacuum-applied technology has been carried out by a kind of batch process.
That is, one batch process includes three steps of: a first setup step in which a roll of material film (generally, 100-200 μm in thickness), vapor source and winding shaft for winding a deposited film are set up in a vacuum chamber, and thereafter the vacuum chamber is closed and decompressed so as to attain a degree of vacuum sufficient enough for the process; a step in which the metallic layer is formed on one side of the film with feeding the film; and a second setup step in which the decompression is removed, the deposited film roll is taken out, and the interior of the vacuum chamber is cleaned.
Since the step for forming the metallic layer can be carried out with a rate of 200-300 meters/minute in case of the vacuum evaporation method, therefore this step can be finished within about several minutes to ten minutes per one roll (1000-2000 meters per one roll).
In contrast, a total period of time required for the setup steps including the first and second setup steps is several tens times as long as the period of time required for the step for forming the metallic layer. Especially in a case of the vacuum evaporation of a special metal such as indium, which enables deep drawing upon molding, not like a normal metal such as aluminum, the total period of time described above becomes even longer.
Since the work in the setup steps is mainly carried out by hand, therefore it accounts for almost all of the cost of forming the metallic layer. However, the setup steps can hardly be simplified easily and the cost of the setup steps can hardly be reduced easily.
A metallically decorated sheet has to be improved in design and scratch resistance.
Regarding the design, etching processing, hair-line finish or so-called “sand-mat processing” can be applied solely or in combination to a surface of a transparent or translucent thermoplastic resin film, which is to form a metallic layer, at the metallic layer side, thereby the design can be improved freely. However, when the metallic layer is formed on the surface subjected to such a processing described above, adhesion property between the metallic layer and the resin film deteriorates, resulting in that the metallic layer peels off from the resin film, for example, upon molding, thereby a defective product arises. Here, although the processing described above can be applied to the opposite side of the resin film, to which the metallic layer is not formed, the effect of such a processing is easily lost on account of friction in this case.
An acrylic resin film may be employed as the transparent or translucent thermoplastic resin film so as to obtain a sufficient improvement in scratch resistance. However, in case of acrylic resin film, the resin film has too low tear strength to be handled well, resulting in that an accident such as a rupture takes place upon formation of the metallic layer, that is, a stable production is difficult.
Further, an acrylic resin film has a poor adhesion property with the metallic layer causing a peeling of the metallic layer, for example, upon molding and therefore, causing a defective product. When indium, in which a deep drawing can be carried out in comparison with aluminum, is employed as a metal to compose the metallic layer, the adhesion property of the metallic layer with an acrylic resin film is poorer than that in the case of aluminum, that is, the resulted product may have many defective portions where no metallic luster can be seen.
A metallically decorated sheet has been investigated, in which by using a polyolefin film or polyester film the metallic layer is formed on one side followed by laminating it onto the base film. However, the polyolefin film or polyester film has low scratch resistance causing a flaw arising on a surface of the molded product molded by using the metallically decorated sheet. Further, when the polyolefin film or polyester film is employed, the molding property deteriorates, therefore a molded product can not be obtained, in which the expressivity of details of the molded product is excellent.
Then, a hard coating layer by using a hard coating agent is formed on a metallically decorated surface of a molded product or an intermediate molded product, in which a metallically decorated sheet is molded by heat forming method such as vacuum forming. The surface hardness of the product is improved as a result. Here, the intermediate molded product is defined as a matter, which is in advance formed in a shape of the inner walls of the cavity of the mold or in a similar shape by using heat forming and so on, and is further to be inserted into a mold as an insert upon injection molding of the molded product and becomes integral with the molded product after the molding of the molded product. In this specification, both of a molded product and an intermediate molded product are called molded product.
The hard coating layer described above is several to several tens μm in thickness. A hard coating agent dissolved in an appropriate solvent or an emulsion of a hard coating agent is prepared, then it is applied onto a surface of the molded product or intermediate molded product by using spray-coating method or immersion-coating method and then, the hard coating layer is formed being cured by heating method or ultraviolet irradiation method.
However, the hard coating layer causes various problems as shown below:
(1) Equipment for spray-coating, immersion-coating, ultraviolet irradiation or heating is necessary.
(2) In the coating process, dust or dirt tends to adhere to the film causing deterioration in yield. A special and expensive facility such as a clean room may be necessary.
(3) The hard coating process has to be carried out not by a continuous process but by a batch process per molded product, causing the necessity of time, deterioration in productivity and a great deal of material loss.
(4) A uniform formation of the hard coating layer is difficult, that is, non-uniform surface hardness and spots in appearance for the product tend to result. Especially, in a case that the shape of the surface of the molded product, onto which the hard coating layer is to be formed, is complicated, a uniform hard coating layer actually can not be attained.(5) The stock, conveyance and control for the molded product, to which the hard coating is to be applied, require a cost.(6) The hard coating layer is formed on a portion (e.g. the back side) where the coating is unnecessary. For a portion to which the coating must not be applied, the masking becomes necessary before the coating, causing the necessity of time and a cost.(7) When the hard coating agent of ultraviolet curing-type is employed, the hard coating layer has poor weather resistance. On the other hand, when the hard coating agent of thermoplastic type is employed, the molded product may possibly be heat-deformed, curved or twisted. Therefore, the hard coating agent must be selected according to the purpose, shape and resin to be used.
Furthermore, in addition to the primary effect of giving a metallic appearance, the metallically decorated sheet is required to have good scratch resistance or various design performances (including color) at the same time. Therefore, the production of the metallically decorated sheet tends to be a type of many varieties and small amount of production, causing the problem in control of the stock and that in a cost.